Is there a way Blender can export to PDF(.U3D)?
I cannot see it in the the list of Import/Export. However, you can convert to another format, and use an additional tool. These formats can be read/written by Meshlab: PLY, STL, OFF, OBJ, 3DS, VRML 2.0, U3D, X3D and COLLADA. Export as one one of the highlighted formats, import it into Meshlab, and export to U3D.